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Jul 27, 2021, 11:12 PM
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Connect Servos to Whoop FC


Connect Servos to Whoop FC (0 min 18 sec)

  I tried to connect 2 servos to Whoop FC, Crazybee F3 FR, which I happened have as an FC
for UR65 Frsky Version. I know there are other newer and better Whoop FCs, but I used this
as I happened to have.

〇Where should I connect servos?
My version of Craybee F3 FR has pads for TX3, RX3 which I don't use. TX3 and RX3 are connected to
PB10 and PB11 of the MCU, respectively. To use servos, they have to be assigned to timer output
ports. Fortunately they can be assigned to TIM2_CH3(AF1) and TIM2_CH4(AF1). Problem was that
Motor3 and Motor4 which are conneted to PA3 and PA2 were also assigned to TIM2_CH4 and TIM2_CH3
in default. So I reassigned them to TIM15_CH2(AF9) and TIM15_CH1(AF9). If I were able to use cli timer
command, those setting would be:

resource servo 1 B10
resource servo 2 B11
timer A03 AF9
timer A02 AF9
timer B10 AF1
timer B11 AF1

But unfortunately Betaflight doesn't support timer command for old F3 target. So I modified target.c
and target.h in source code of Betaflight 3.5.1 to change those timer settings.

target/CRAZYBEEF3FR/target.c
DEF_TIM(TIM2, CH4, PA3, TIM_USE_MOTOR, 0),
DEF_TIM(TIM2, CH3, PA2, TIM_USE_MOTOR, 0),

DEF_TIM(TIM15, CH1, PA3, TIM_USE_MOTOR, 0),
DEF_TIM(TIM15, CH2, PA2, TIM_USE_MOTOR, 0),
DEF_TIM(TIM2, CH3, PB10, TIM_USE_SERVO, 0),
DEF_TIM(TIM2, CH4, PB11, TIM_USE_SERVO, 0),

target/CRAZYBEEF3FR/target.h
#define USABLE_TIMER_CHANNEL_COUNT 4

#define USABLE_TIMER_CHANNEL_COUNT 6

〇Airplane also needs to hover.
Whoop will hover in Horizon Mode but airplane won't. I modified Horizon Mode slightly
to hold aircraft vertically. It works like an auto hover mode of airplane gyro.
Acc_trims can be used by stick commands like Whoop.

〇hex file
I attached a hex file which I used for activating 2 servos and modified Horion Mode. No Warranty.

〇Betaflight setting
I made an airplane with 2 motors and 2 servos. After chosing flying wing I used cli command for
differential thrust and insignificant settings. I connected motors to top left and top right connectors.

mixer CUSTOMAIRPLANE
mmix reset
mmix 0 1.000 0.000 0.000 0.300
mmix 1 1.000 0.000 0.000 -0.300
smix reset
smix 0 2 0 -100 0 0 100 0
smix 1 3 0 -100 0 0 100 0
smix 2 2 1 -100 0 0 100 0
smix 3 3 1 100 0 0 100 0
resource motor 1 A02 #top left
resource motor 2 B09 #top right
resource SERIAL_TX 3 none
resource SERIAL_RX 3 none
set servo_lowpass_hz=5
set small_angle =180

Have a safe flight.

〇Specs
FC : Happymodel Crazybee F3 FR
Motors : Happymodel SE0802 25000KV x 2
Prop : GemFan 1219-3 x 2
Servos : 1.7g 1s servo x 2
Battery : 1s 220mAh 30-60C HV
Size : 40.5cm(L) x 26cm(W)
AUW : 30g
Last edited by aero nishi; Aug 09, 2021 at 05:00 PM.
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